1. Field of the Invention
The present invention relates to processes to provide uretonimine-modified isocyanate composition and to uretonimine-modified isocyanate composition.
2. Background Information
Organic isocyanate compositions are well known in the art. Several compositions, in particular the ones comprising methyl diphenylisocyanate isomers (MDI isomers), and most in particular the MDI compositions comprising a high amount of 4,4′MDI, are solid. To provide liquid compositions, typically the composition is modified by introducing uretonimine-groups, this is done by reacting all or part of the organic isocyanate composition over a catalyst, whereby first carbodiimide groups are proved, which on their turn further react with isocyanate groups to provide uretonimine groups.
This reaction must be terminated by the addition of so-called catalyst killers, quenching agents or stopping agents.
Typically, acid chlorides are mentioned as catalyst stoppers in EP 0193787, EP 0189156, EP 0308710, U.S. Pat. No. 7,030,274, U.S. Pat. No. 6,120,699, U.S. Pat. No. 4,424,288 and U.S. Pat. No. 4,088,665. In WO 2008/040722 and U.S. Pat. No. 6,489,503, a backblending process is described wherein the catalyst killer being oxalylchloride is mentioned.
In U.S. Pat. No. 4,014,935, the addition of PC15 as catalyst stopper results in a water clear liquid. PC15 is a powder which is very toxic and difficult to handle.
In EP32011A1, carbodiimine-modified isocyanate is provided by reacting the isocyanate composition over a catalyst, whereby carbodiimide groups and uretonimine groups are proved. These two components form part in a reversible reaction ofcarbodiimine group+isocyanate group⇄uretonimine group.
The catalyst used to provide the carbodiimine groups is stopped by the addition of a catalyst killer, in particular thionyl chloride. The equilibrium reaction is forced to the carbodiimine side (i.e. the amount of uretonimine groups is reduced) by reacting carbodiimine groups with a diester of an aliphatic dicarboxylic acid in the presence of oxalic or formic acid. Carbodiimine groups having reacted with the diester, does not form part anymore in the equilibrium reaction. The amount of uretonimine in the isocyanate can be brought to substantially zero.
In WO2008/009669, the use of oxalyl chloride as catalyst quencher is suggested. This catalyst quenching or killing agent is toxic and had a boiling point of about 63 deg C. as the quenching typically is to be done at temperatures of about 80 to 110 deg C., oxalyl chloride is difficult to handle.
WO2007/006622 suggests the use of adipoylchloride as catalyst killing agent. It was also noticed that uretonimine modified isocyanates wherein adipoyl chloride was used as catalyst killer, may become less stable, i.e. the catalyst still in the composition, may regain part of its activity. This can cause the creation of CO2 in the stored isocyanate containers, and may cause a potential safety risk when opening the containers.
It is an object of the present invention to provide an alternative method to provide uretonimine-modified isocyanate composition, which overcomes, at least partially, some or all drawbacks of prior art. Embodiments of the present invention provide uretonimine-modified isocyanate composition which are water clear, using less or even non toxic catalyst killers, while providing a stable product.
The above objective is accomplished by a method according to the present invention.